The present invention relates to a multi-level resist process, and more particularly to a method for forming the pattern utilizing an inorganic material.
FIGS. 1a to 1d are to show a conventional process for forming the pattern of multi-level resist, in case that any step is not existed.
As shown in FIG. 1a, first, a bottom resist film 13, an inter-layer 15 and a positive top resist film 17 are coated on a semiconductor 11, in this order.
The bottom resist film 13 and the top resist film 17 are organic resists and the inter-layer 15 is made of one of spin on glass(SOG) film and PE oxide film, as an insulating film.
As shown in FIG. 1B, the top resist film 17 is exposed by a light source 21, using a pattern mask 19.
Since the exposed portion of positive top resist film 17 is removed upon performing a development process, the pattern of positive top resist film 17 is formed.
Subsequently, the inter-layer 15 and the bottom resist film 19 are etched to form a multi-level resist(MLR) pattern 23, using the pattern of top resist film 17 as an etch mask.
The MLR pattern 23 will be served as an etch mask, upon etching a polysilicon film, metal film and oxide film which are used as lower layers.
According to Conventional methods for forming a MLR pattern using an organic resist, a polymer 25 is formed at the side walls of MLR pattern 23 by the reaction of Cl.sup.- upon etching the top resist film 17 made of organic material.
Therefore, since the MLR pattern 23 has the bias of irregular line width in accordance with the degree in concentration and the micro-loading effect is thus caused, there is a disadvantage in that it is difficult to adjust critical dimension.
FIGS. 2A to 2D are to show a conventional process for forming the MLR pattern utilizing an organic resist, in case that steps exist.
Referring to FIG. 2A, there is illustrated a semiconductor device such as a three-dimensional capacitor cell which has a surface comprising flat portions P and recess portions R.
As shown in FIG. 2A, the steps are occurred between the flat portions P and the recess portions R of the surface.
Subsequently, a MLR planarization process is carried out to the above-steps.
That is, a bottom resist film 35 made of an organic material is thickly deposited on the whole surface of substrate.
An insulation film such as SOG film or PE oxide film is formed on the bottom resist film 35 as an inter-layer 37 and a top resist film 39 made of an organic material is then deposited on the inter-layer 37.
At this time, the top resist film 39 has a positive type.
Although the MLR planarization process is carried out, the whole surface is not planarized completely due to the steps at the surface of the semiconductor device.
Referring to FIG. 2B, the MLR planarization process is performed and a contact hole is then defined, using a pattern mask 41.
Upon performing an exposure by a light source 43 to define the contact hole, the surface area of the top resist film 39 being exposed by the light source 43 becomes different at the flat portions P and the recess portions R which are occurred due to the steps of surface.
Referring to FIG. 2C, a process same as the MLR pattern of FIG. 1 is carried out to form a MLR pattern 45.
In case that steps are existed, however, since the surface area of the top resist film 39 being exposed at the flat portions P and the recess portions R becomes different as shown in FIG. 2D, it is difficult to exactly obtain the MLR pattern having a desired width.
As shown in FIG. 2E, it is therefore impossible to obtain a contact hole 47 having a desired size although a contact hole 47 is formed by etching the semiconductor device which is the bottom layer of MLR pattern 45, using the MLR pattern 45.
That is, FIG. 2 is to show a plan view to the contact hole 47, the size of contact hole at the recess portions R is different from that of the flat portions P.
Therefore, according to the conventional method for forming a MLR pattern using an organic resist, there is an disadvantage in that the surface is not planarized even after the planarization process is completed, in case that the steps of semiconductor device is above about 1.5 .mu.m.
As shown in FIG. 2B, since the steps of semiconductor device which is the bottom layer are maintained to the top layer, it is impossible to form the desired pattern exactly.
Since the organic resist film is also used identically, even in case that the steps are existed, the polymer is formed at the side planes of MLR pattern as shown in FIG. 1, thereby causing the shape of contact hole itself to be deformed.